1. Field of Invention
The invention relates to a developing cartridge which is applied to a laser printer.
2. Description of Related Art
U.S. Pat. No. 6,336,014 discloses a structure where a developing cartridge accommodating toner is detachably attached to a printer. The developing cartridge includes a developing roller that supplies toner to a photosensitive medium and a supply roller that makes contact with the developing roller to supply toner to the developing roller.
The developing cartridge further includes side seals for preventing toner carried on the developing roller from leaking outside from the developing cartridge. The side seals are disposed at both ends of the developing roller with respect to its axial direction so as to make sliding contact with a circumferential surface of the developing roller at the both ends.
The side seals disclosed in U.S. Pat. No. 6,336,014 are made by interposing a polyethylene terephthalate (PET) film between an urethane sponge and a TEFLON® felt, and the surface of the TEFLON® felt makes sliding contact with a circumferential surface of the developing roller.
In the side seals disclosed in U.S. Pat. No. 6,336,014, the PET film is wider than the TEFLON® felt and is caught in between the supply roller and the developing roller. In other words, the PET film can prevent toner in the developing cartridge from directly making contact with the TEFLON® felt.
However, the supply roller is usually made of a sponge. When the PET film makes sliding contact with the circumferential surface of the supply roller, the surface of the supply roller is liable to sustain damage. If a sponge chip of the supply roller gets into the toner, it will deteriorate image quality.